Driving circuit, illumination light source, and illumination device

Abstract

A driving circuit includes a rectifying and smoothing circuit that rectifies an AC dimming signal, and a voltage conversion circuit including: a switching element having a source connected to a low-potential output terminal of the rectifying and smoothing circuit; a diode having an anode connected to a high-potential output terminal of the rectifying and smoothing circuit; an inductor disposed between the diode and a drain of the switching element; an oscillation controller; a capacitor that is charged by receiving magnetic energy from the inductor when the switching element is OFF, and discharges to a load when the switching element is ON; and a power control circuit that applies a voltage corresponding to a voltage at a high-potential terminal of the capacitor to the oscillation controller as a supply voltage for driving the oscillation controller.

The invention claimed is: 
     
       1. A driving circuit that converts a phase-controlled AC dimming signal into a DC signal according to a dimming level, and causes a light-emitting device to emit light, using the DC signal, the driving circuit comprising:
 a rectifying circuit that rectifies the AC dimming signal; and 
 a voltage conversion circuit that is connected between a low-potential output terminal and a high-potential output terminal of the rectifying circuit, and converts an input voltage from the rectifying circuit and applies a DC voltage to the light-emitting device, 
 the voltage conversion circuit including: 
 a switching element having one end connected to the low-potential output terminal of the rectifying circuit; 
 a first diode having an anode connected to the high-potential output terminal of the rectifying circuit; 
 a first inductor having one end connected to a cathode of the first diode, and another end connected to another end of the switching element; 
 an oscillation controller that controls a pulse signal to be supplied to a control terminal that controls ON and OFF of the switching element; 
 a first capacitor that is charged by receiving magnetic energy from the first inductor when the switching element is OFF, and discharges to the light-emitting device when the switching element is ON; and 
 a power control circuit that is connected to a high-potential terminal of the first capacitor and applies a voltage at the high-potential terminal of the first capacitor to the oscillation controller to stabilize a supply voltage for driving the oscillation controller, 
 wherein the driving circuit alternates between a first state and a second state, the first state being a state in which when the switching element is ON, the first capacitor discharges and the magnetic energy is stored in the first inductor with a current flowing from the rectifying circuit to the first inductor through the first diode, the second state being a state in which when the switching element is OFF, the magnetic energy stored in the first inductor is discharged to the first capacitor, and the current flows from the rectifying circuit to the first inductor through the first diode to compensate for the magnetic energy discharged from the first inductor, and 
 wherein the first capacitor, when discharging to the light-emitting device when the switching element is ON, stabilizes the supply voltage for driving the oscillation controller. 
 
     
     
       2. The driving circuit according to  claim 1 , further comprising:
 a second inductor having one end connected to the one end of the first inductor, and another end connected to a cathode of the light-emitting device; and 
 a second diode having an anode connected to the another end of the first inductor, and a cathode connected to the high-potential terminal of the first capacitor, 
 wherein the high-potential terminal of the first capacitor is connected to an anode of the light-emitting device and to an input terminal of the power control circuit, and 
 the first capacitor has a low-potential terminal connected to the low-potential output terminal of the rectifying circuit. 
 
     
     
       3. The driving circuit according to  claim 1 , further comprising:
 a second capacitor inserted in series between the cathode of the first diode and the one end of the first inductor; 
 a second diode having an anode connected to a connecting point between the first diode and the second capacitor, and a cathode connected to the high-potential terminal of the first capacitor; 
 a second inductor having one end connected to the another end of the first inductor, and another end connected to the cathode of the second diode; and 
 a third diode having an anode connected to the another end of the first inductor, and a cathode connected to an anode of the light-emitting device, 
 wherein the high-potential terminal of the first capacitor is connected to an input terminal of the power control circuit, and 
 the first capacitor has a low-potential terminal connected to the low-potential output terminal of the rectifying circuit. 
 
     
     
       4. The driving circuit according to  claim 1 , further comprising:
 a second inductor having one end connected to the another end of the first inductor, and another end connected to a cathode of the light-emitting device; 
 a second diode having an anode connected to the cathode of the first diode, and a cathode connected to the high-potential terminal of the first capacitor; and 
 a third diode having an anode connected to the another end of the first inductor, and a cathode connected to the high-potential terminal of the first capacitor, 
 wherein the high-potential terminal of the first capacitor is connected to an anode of the light-emitting device and to an input terminal of the power control circuit, and 
 the first capacitor has a low-potential terminal connected to the low-potential output terminal of the rectifying circuit. 
 
     
     
       5. The driving circuit according to  claim 1 ,
 wherein the power control circuit includes: 
 a first resistor element having one end connected to the high-potential terminal of the first capacitor, and another end connected to a power supply terminal of the oscillation controller; and 
 a Zener diode having an anode connected to the low-potential output terminal of the rectifying circuit, and a cathode connected to the power supply terminal. 
 
     
     
       6. The driving circuit according to  claim 5 ,
 wherein the power control circuit further includes a second resistor element having one end connected to the high-potential output terminal of the rectifying circuit, and another end connected to the power supply terminal. 
 
     
     
       7. The driving circuit according to  claim 1 , further comprising
 a dimming signal detection circuit that applies to the oscillation controller a dimming signal voltage corresponding to a voltage obtained by rectifying the AC dimming signal by the rectifying circuit, 
 wherein the oscillation controller controls the pulse signal based on the dimming signal voltage. 
 
     
     
       8. The driving circuit according to  claim 7 ,
 wherein the dimming signal detection circuit includes: 
 a third resistor element having one end connected to the high-potential output terminal of the rectifying circuit, and another end connected to an input terminal of the oscillation controller to which the dimming signal voltage is applied; 
 a fourth resistor element having one end connected to the input terminal of the oscillation controller, and another end connected to the low-potential output terminal of the rectifying circuit; and 
 a third capacitor having one end connected to the input terminal of the oscillation controller, and another end connected to the low-potential output terminal of the rectifying circuit. 
 
     
     
       9. An illumination light source, comprising:
 a light-emitting device; and 
 a driving circuit that converts a phase-controlled AC dimming signal into a DC signal according to a dimming level, and causes the light-emitting device to emit light, using the DC signal, 
 wherein the driving circuit includes: 
 a rectifying circuit that rectifies the AC dimming signal; and 
 a voltage conversion circuit that is connected between a low-potential output terminal and a high-potential output terminal of the rectifying circuit, and converts an input voltage from the rectifying circuit and applies a DC voltage to the light-emitting device, 
 wherein the voltage conversion circuit includes: 
 a switching element having one end connected to the low-potential output terminal of the rectifying circuit; 
 a first diode having an anode connected to the high-potential output terminal of the rectifying circuit; 
 a first inductor having one end connected to a cathode of the first diode, and another end connected to another end of the switching element; 
 an oscillation controller that controls a pulse signal to be supplied to a control terminal that controls ON and OFF of the switching element; 
 a first capacitor that is charged by receiving magnetic energy from the first inductor when the switching element is OFF, and discharges to the light-emitting device when the switching element is ON; and 
 a power control circuit that is connected to a high-potential terminal of the first capacitor and applies a voltage at the high-potential terminal of the first capacitor to the oscillation controller to stabilize a power supply voltage for driving the oscillation controller, and 
 wherein the driving circuit alternates between a first state and a second state, the first state being a state in which when the switching element is ON, the first capacitor discharges and the magnetic energy is stored in the first inductor with a current flowing from the rectifying circuit to the first inductor through the first diode, the second state being a state in which when the switching element is OFF, the magnetic energy stored in the first inductor is discharged to the first capacitor, and the current flows from the rectifying circuit to the first inductor through the first diode to compensate for the magnetic energy discharged from the first inductor, and 
 wherein the first capacitor, when discharging to the light-emitting device when the switching element is ON, stabilizes the supply voltage for driving the oscillation controller. 
 
     
     
       10. An illumination device, comprising:
 a light-emitting device; 
 a driving circuit that converts a phase-controlled AC dimming signal into a DC signal according to a dimming level, and causes the light-emitting device to emit light, using the DC signal; and 
 a dimmer that generates the AC dimming signal using an AC power supply, 
 wherein the driving circuit includes: 
 a rectifying circuit that rectifies the AC dimming signal; and 
 a voltage conversion circuit that is connected between a low-potential output terminal and a high-potential output terminal of the rectifying circuit, and converts an input voltage from the rectifying circuit and applies a DC voltage to the light-emitting device, 
 wherein the voltage conversion circuit includes: 
 a switching element having one end connected to the low-potential output terminal of the rectifying circuit; 
 a first diode having an anode connected to the high-potential output terminal of the rectifying circuit; 
 a first inductor having one end connected to a cathode of the first diode, and another end connected to another end of the switching element; 
 an oscillation controller that controls a pulse signal to be supplied to a control terminal that controls ON and OFF of the switching element; 
 a first capacitor that is charged by receiving magnetic energy from the first inductor when the switching element is OFF, and discharges to the light-emitting device when the switching element is ON; and 
 a power control circuit that is connected to a high-potential terminal of the first capacitor and applies a voltage at the high-potential terminal of the first capacitor to the oscillation controller to stabilize a power supply voltage for driving the oscillation controller, and 
 wherein the driving circuit alternates between a first state and a second state, the first state being a state in which when the switching element is ON, the first capacitor discharges and the magnetic energy is stored in the first inductor with a current flowing from the rectifying circuit to the first inductor through the first diode, the second state being a state in which when the switching element is OFF, the magnetic energy stored in the first inductor is discharged to the first capacitor, and the current flows from the rectifying circuit to the first inductor through the first diode to compensate for the magnetic energy discharged from the first inductor, and 
 wherein the first capacitor, when discharging to the light-emitting device when the switching element is ON, stabilizes the supply voltage for driving the oscillation controller.